M1 Gear Oil not as good anymore?

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Leo

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I recently flushed out the TC & rear diff in my Evo X with Mobil 1 Synthetic Gear Lubricant LS 75W-90 and I couldn't help but notice some of its stats aren't that impressive:

Pour Point, ºC (ASTM D97) -39
Flash Point, ºC (ASTM D92) 150

Its much worse than their own M1 Delvac 75w90 and many other synthetic GL5 lubes such as Amsoil SVG with PPs 200c. Motul Gear 300 absolutely blows M1 away. Funnily the M1 75w90 LS has absolutely no OEM approvals besides GL5 too. Why?

Has M1 dropped the ball and cheapened out with the new "LS" formulation? I trust Mobil would never make a subpar M1 product but it does seem a little suspect.
 
M1 is cheaper than both Amsoil and Motul to start. Do you plan on running your vehicle in temperature colder than -39C or hotter than 150C? If not, then why worry?

What other 75W90 LS has OEM approval? Certainly not Motul nor Amsoil.
 
Why would a flash point of 150C be an issue in a differential? I think you'd have far bigger things on your mind if it was getting anywhere near those temperatures.
 
M1 gear lub has served myself and others I know very well with never a parts failure even in 100s of Ks.
 
I sense a bit of derailment... I have no doubt concerning its excellent abilities as a gear lubricant.

The enquiry is why the specs are far below par compared to other synthetics available, and on par or even worse than many dino or semi-synth gear lubricants? It seems a little odd for a Mobil 1 product, especially when the Delvac equivalent appears far superior.

(At BITOG we split hairs over much smaller differences in PP for engine oils!)
 
I have the M1 in my Cruiser with ARB lockers and it seems to work well. The Delvac would be a good choice too for heavy duty work.

But the M1 probably gives slightly better MPG's due to lower viscosity at 40/100C temps and a better VI.

I imagine both will work great.

My Toyota only specifies GL-5 so the other OEM approvals don't matter to me.
 
I emailed a copy of your narrative to Mobil 1, here is their answer:

The pour point and flash point are not the most important aspects of the
product. The real test is in the performance of the product. As far as
the OEM specs, we offer a few products that meet different requirements
to fit the needs of consumers. Often products do not carry ratings not
because they do not meet them but because they just have not been tested
for it due to the use of the product by the consumer.
 
Originally Posted By: cchase
Why would a flash point of 150C be an issue in a differential? I think you'd have far bigger things on your mind if it was getting anywhere near those temperatures.


Have you ever put your hand on a differential after a hard, hot, long drive?
 
Originally Posted By: Pablo
Originally Posted By: cchase
Why would a flash point of 150C be an issue in a differential? I think you'd have far bigger things on your mind if it was getting anywhere near those temperatures.


Have you ever put your hand on a differential after a hard, hot, long drive?


I have never touched a differential that felt anywhere near 300 degrees F. I'm sure they're out there somewhere.
 
Hi,
cchase - I have some experience in this area!

Originally Posted By: cchase

I have never touched a differential that felt anywhere near 300 degrees F. I'm sure they're out there somewhere.


Most commercial axle Manufacturers set an operating limit below 250F (120C). Intermittent temps to 300F (149C) in extremet circumstances may be permitted - these would require a much shorter OCI and typically call for a synthetic lubricant

In my testing and actual use programmes (US and German axles) the following temperatures were encountered in an ambient range of from -5C to +45C

Heavy trucks (42500kgs+ - 110kmh speeds)
Average Gearbox = 86C (Hi 100C loaded on long 10% gradient)
Average Diffs = 94C (Hi 102C loaded on 10% gradient)

Cars and 4WD SUVs/Utes
Average Diffs = 60 (Hi 85C loaded on gradients)

My testing showed the axle Manufacturers that they were indeed generally using/specifying lubricants of too high a viscosity

Mostly for instance a 75W-90 synthetic was found to be more capable/durable than a mineral 85W-140 at ambient temperatures above 38C (100F)

Maybe there are diffs that exceed 300F (149C) in use - in my years in dealing with road trains (up to >120000kgs) and the likes here I have neaver measured any!
 
Originally Posted By: cchase

I have never touched a differential that felt anywhere near 300 degrees F. I'm sure they're out there somewhere.


Well of course you have not but tests are typically worst case. Say it gets to 250°F, you'll need a little room for margin.
 
Originally Posted By: Pablo
Originally Posted By: cchase

I have never touched a differential that felt anywhere near 300 degrees F. I'm sure they're out there somewhere.


Well of course you have not but tests are typically worst case. Say it gets to 250°F, you'll need a little room for margin.


Still, the take-away here (and my point initially) is that the flash point of 150C is likely not an indicator of a subpar lubricant - it's not something that you can use as a "marker" of quality for this application.
 
Originally Posted By: tig1
M1 gear lub has served myself and others I know very well with never a parts failure even in 100s of Ks.

Was that Kelvins?
 
Driving my Unimog a long distance on flat terrain on a 95F day, the rear diff housing temp was measured at ~200F. That was at about 59mph for >2hrs, with rear axle load ~8000kg (about 17600 lb), GAWR 9000kg, with only a 2.5L capacity of synthetic 75W90 (Delvac). It has a small capacity because there are portal boxes at the hubs with gear ratio 2.71 (diff is only 2.18, for a net of 5.92), which hold 700cc each.
The portals were only 140F.
The front diff (it is full time 4WD) was about 180F.

Charlie
 
Last edited:
If you can get a gear hot enough to lose temper, some things are getting a little hotter than 150C, at least some of the time. I would expect that the oil temps and the housing surface temps never reach the same temperature as the gear teeth surface temps.
 
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